Decision Tables:
Decision table is a tool used in solving complex program logic. It uses a tabular format to represent the work statement of a problem. The decision tables are extremely useful when a program involves a large number of decisions.
As it is easier to draw and change
the charts so decision tables are used in place of flowcharts. Moreover, the
decision tables also provide compact documentation. However, due to
difficulties involved in designing a flowchart they are not considered a common
tool for program solving by the beginners.
Now
before drawing the decision table, we should first identify all the condition
statements and the corresponding actions to be taken.
The various conditions are:
Count
<=10
Percentage>=50
Percentage<60
The various actions that can
be taken are:
Calculate
Percentage
Write
Count
Add
1 to STU Count
Read
next student record
Stop
We
shall now arrange these condition statements and actions into a decision table
as shown:
Each
decision table has 6 parts, the Table
Heading portion, the Decision Rule
Number, the condition Stub that
list the various condition statements, the Action
Stub that list the various actions that can be taken, the Condition Entries Portion and the Action Entries portion. The condition
entries are expressed by Y and N used for yes and No respectively.
The action entries are represented by X mark.
In
the above table, four rules are being made. These are discussed as follows:
Rule 1: If COUNT <= 10 and PERCENTAGE is not greater than
equal to 50 then computer should read the next student’s record.
Rule 2: If COUNT <= 10 and PERCENTAGE >= 50 , are true
but PERCENTAGE is less than 60 is false then again computer should read the
next students record.
Rule 3: If COUNT >=10 and PERCENTAGE >=50 and PERCENTAGE
<60 , it is true then computer should add 1 to STUCOUNT and read next
student’s record.
Rule 4: If COUNT <=10 is false then computer should print
STUCOUNT and STOP.
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